Pump



lard! 1950 u. L. HOPPER 1 2,499,645 PUHP Filed May 24, 1946 lNVENTOR A ATTORNEY Patented Mar. 7, 1950 UNITED STATES PATENT OFFICE PUMP , Dwight L. Hopper, Pittsburgh, Pa., assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application May 24, 1946, Serial N 0. 671,974

3 Claims. 1

My invention relates to a diffusion pump, and particularly to a heating element for an oil diffusion pump having high heat requirements.

In the operation of vacuum pumps of the oil diffusion type, it is customaryto provide a volatile oil and apply heat thereto to produce the entraining or pumping vapors. With the increase in pumping speeds as Well as the differential pressures against which the pumps are operated, it is necessary to supply ever increasing quantities of heat to the vaporizing material.

Difiiculty has been experienced either in passing necessary heat into the boiler or in excessive deleterious distillation of the vapor producing material. In order to eliminate this difiiculty, I have provided an internal heater composed of a bare heating element or Wire of relatively great length and large cross sectional area immersed directly in the vapor producing material and supported in insulated relation from the container Walls, it being desirable to support the heating element in such manner that very small portions of the heating element are in contact with the insulating support in order to prevent spot temperatures of excessive value which would produce destructive distillation of the vapor producing material.

It is, accordingly, an object of my invention to provide a heating element directly in contact with the vapor producing materials.

It is a further object of my invention to provide a heating element having a low watt density per unit area of the heating element.

It is a further object of my invention to provide a heating element suspended in substantially oil immersed position in the boiler.

Other objects and advantages of my invention will be apparent from the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure 1 is a plan View of a heating element according to my invention;

Fig. 2 is a sectional elevation of a portion of a pump embodying my invention; and

Fig. 3 is a fragmentary illustration of a modification according to my invention.

In the preferred embodiment of my invention, the heating element l is composed of a relatively stable resistance material, preferably such as the alloys now sold under the name Nichrome and comprising a wire or preferably a ribbon of relatively large surface area per unit of length to produce a relatively low wattage output per unit of the surface area of the heating element.

This heating element l is wound into a continuous spiral with the ends 2 and 3 supported on lead-in structures 4 and 5 extending through the Wall 6 of the boiler container. Preferably these lead-in structures 4 and 5 are of the insulated bushing type shown in Patent No. 2,300,941. In order to provide insulation between the wire I and the side 6 of the boiler ceramic supports ID are provided secured permanently to the bottom of the boiler. Supporting grooves II are provided in the upper surface of the ceramic insulators l0, the shape of the grooves ll being such that the heating element 1 makes a three point contact with the insulating material l0. That is, at the entering and exit edges from the groove H, the contact element Will make a point contact with the inside edge l2 of the groove ll while at substantially the central portion of the groove H, the heating element I will make a point contact with the outside edge |3 of the groove II. In this manner, oil l5 may flow freely around substantially the entire surface of the heating element l and thus prevent excessive hot spots which might burn out the heating element l or cause destructive distillation of the vapor producin fluid l 5.

Instead of using fixed bar type insulating supports If), it is possible to provide a plurality of bead-like elements 20 to support the heating element I. In the event such bead-like elements 2 are used, it is necessary to provide these elements with relatively large interior openings 2| so that the heating element l makes very limited contact with the inner surface of the insulating beads 20 and allows the insulating oil I5 to flow freely around all portions of the heating element 1.

While for purposes of illustration I have shown and described preferred embodiments of my invention, it will be apparent that changes and modifications can be made therein Without departing from the true spirit of my invention or the scope of the appended claims.

I claim as my invention:

1. In a boiler for a vacuum pump a heating element immersed in the vaporizing material, said heating element being in direct contact with said vaporizing material, insulated lead-in terminals for said heating element, insulating means for supporting said heating element out of contact with the walls of said boiler, said supporting elements making a three point contact with said heating electrode.

2. A heating element for a vapor evolving boiler comprising a metallic container, a quantity of vapor evolving material in said container,

a metallic heating element in direct contact with said. vaporizing material, insulated lead-in terminals for said heating element and insulating supports for said heating element, said insulating supports making spaced apart point contacts with said heating element whereby the vaporizing material comes into contactwith the maximum portion of the surface of said heating element.

3. A heating element for a vapor evolving boiler comprising a container of conducting material, a quantity of vapor evolving oil in said sistor, ceramic insulator supports for said resistor, said supports having grooves making three point contact with said resistor.

DWIGHT L. HOPPER.

REFERENCES CITED The following references are: of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 403,110 Johnson et a1 May 14, 1889 12381243 Frickey- Aug. 28, 1917 1,939,125: Lubbock et a1 Dec. 12, 1933 Stuck-'1 Nov. 2, 1937 

